I. Field of Invention
The invention concerns the design of a selective pipe reactor and a plant for producing various mixtures facing a common problem, how to preferentially react an acid and a base within a flow of a heat and/or acid sensitive component or mixture of components without decomposing them, or decomposing preferentially one of the components. A reactor that could be used for production of urea ammonium sulphate (UAS) is of special interest.
II. Description of Related Art
Pipe reactors for manufacturing of ammonium salts are for example known from U.S. Pat. No. 2,568,901, U.S. Pat. No. 2,755,176 and U.S. Pat. No. 5,904,906. These reactors make is possible to react an acid and a base, but these reactors cannot be used for a reaction where a third component is introduced.
Current commercial production of urea ammonium sulphate (UAS) is accomplished by physically mixing the two compounds by a process of adding pulverized solid ammonium sulphate to molten urea in a granulation step, such as a drum or a pan, as described in U.S. Pat. No. 3,785,796. This can be called the “solid route”. It appears to be a rather simple process. It presents however some serious drawbacks both from an economical and from a process point of view.
Ammonium sulphate (AS) synthesis reaction in urea solution is described in U.S. Pat. No. 3,928,015 as a reaction in two steps. A bisulphate solution and ammonia react in the urea solution to produce essentially anhydrous AS in admixture with molten urea in a simple and inexpensive tank type or pipe type reactor.
Bisulphate corresponds to the product made by reacting one mole of sulphuric acid with one mole of ammonia, whereas ammonium sulphate corresponds to the product made by reacting one mole of sulphuric acid with two moles of ammonia. The first ammoniation of sulphuric acid (leading to bisulphate) is more exothermic than the second one.
Nevertheless, to perform in situ production of AS in urea solution is a challenge, since the acid promptly reacts with urea leading to urea losses. This significantly limits the advantages of any liquid route versus solid route for the production of UAS, if the losses are too high. Bisulphate is less aggressive to urea than sulphuric acid. According to U.S. Pat. No. 3,928,015, bisulphate is synthesized separately in order to minimize the urea decomposition. By this it does not take the full advantage of the heat released by the first ammoniation.